This invention relates generally to a small printer having selectable character wheels with raised characters around the periphery thereof, and more particularly to an apparatus for controlling a plurality of character wheels with a single electromagnet. The prior art, for example, U.S. Pat. No. 3,848,527, discloses a mechanism for small printers which includes electromagnets which are less in number than the number of printed column positions. An electromagnet is provided for every three column positions, and a selecting roll is provided for controlling the electromagnet so as to select one character wheel at the desired column position. The selection roll makes one-third of a complete revolution in order to select a single character. Therefore, it is necessary that the selecting roll makes one entire revolution before it operates for the three column positions.
Assuming that it takes five milliseconds to select one character, the selecting roll completes one revolution in fifteen milliseconds. Hence, it is rotating at the high speed of four thousand revolutions per minute. Such high speed tends to cause the printer to produce vibrations and noises, and business machines incorporating such a printer have proven unsatisfactory in practical usage. Additionally, the raised characters on the character wheels are displaced for every three columns positions, a feature that prohibits use of character wheels fabricated by ejection molding a material in a common mold. Production of such character wheels requires three different molds and hence, is much more costly. Different molds are likely to produce character wheels having varying character positions resulting from the different molds and misaligned printed characters.
What is needed is a small printer having fewer electromagnets than character wheels, which operates with low vibration and noise and produces printed characters of high quality.